How to make resin coasters

How to make resin coasters

by Kate Ledum

After molding small resin items, you might wonder what to do with them. One possibility is including them in another resin project, such as coasters.

In the tutorial Using Pearl Ex with Resin Two Ways we made a variety of resin leaves. On the side, we also made some shells using the same techniques. These are both perfect for including in a resin coaster.

Other small castings would be good for this technique, too, such as butterflies, ballerinas, flowers, buttons, etc. The items you include in the coaster should be no more than ¼” thick. The items will also need to be smaller than the size of the coaster mold. If you’re putting in multiple items, 1-2” or smaller are recommended. The mold we’ll be using for this project is 4” in diameter and 3/8” deep.

Deciding Which Way the Coaster should face

The first thing you do for a resin coaster project is decide which side you want to be the top of the coaster. Lay the coaster on the table in front of you. Do you want the side facing the table to be the front or top of the finished item, or do you want the side facing you as the top/front? If you want the side facing the table to be the top, you will need to put everything in upside down. If you want the side facing you to be the top, then everything will be facing up. Everything facing you can be easier to arrange since you can see exactly how it is going to look. With everything facing the table, you can lift up the mold and look at it from underneath, but that can be risky while you have liquid uncured resin in it.

The inner surface on this mold is not shiny. That means the finished item will have a matte finish except where the resin is poured in. The pouring side will have a shiny finish. Knowing how the finished item will be can also help you decide.

The coaster mold has a very gently sloped side making the diameter of the mold slightly smaller on the table side. If you make the coaster with the table side up, the top of the coaster will be slightly smaller than the bottom. If you make the coaster with the side facing you as the top, the top will be slightly larger than the bottom. Either way will work well as a coaster.

For this tutorial, the leaves coaster will face toward you and the shell coaster will face the table. For steps which are the same for both coasters, only the Leaves is shown.

Deciding What to Put In the Coaster

Lay the objects you want into the dry mold. Arrange them, rearrange them, and rearrange them again. See how they’ll fit and how you like them placed together. You don’t need to use all the items you have. You can have fewer or more as you want. They can be all one colour or a mix. You can even change your mind a few times as you’re dry fitting them into the mold space.

Since a coaster needs to be flat to do its job, you need to make sure all the items you put in the mold don’t go higher than the edge. One way to do this is to place a piece of paper across the top of the mold, side to side. As long as nothing is touching the top of the paper or poking it up, it should be fine. If something does touch the paper, you can rearrange again to try to nestle it down further or, you may need to set it aside for a different project.

TIP: You can take a picture of how you placed your items in the dry mold to use as a guide when putting them in with the resin later. (Even though I took a picture, I ended up arranging them differently, that’s okay, too.)

Prepare the Mold

Because plastic molds aren’t as flexible as silicone molds and you don’t want to bend your mold so far out of shape you can’t use it again, you should use a mold release to make unmolding easier.

Spray the mold liberally with the mold release and set it aside to dry for at least 30 minutes.

Preparing the Resin

Before you start mixing the resin, you should put on a pair of nitrile or latex gloves. This will protect your hands from the sticky resin. The resin, when cured, is non-toxic.

Easy Cast is a 1:1 two part resin. This means that you pour an equal portion of both part A and part B. For best results measure each part into its own cup before combining them in one cup.

For optimal casting, resin likes a warm, but not hot room. 72-74F is the recommended temperature for working with resin.

Both parts of Easy Cast are thick liquids that become thicker when it’s cold. Resin that’s the consistency of congealed gravy traps bubbles. Since I live in an area that is below the optimum temperature most of the year, I let the resin warm up in warm water bath to help reduce bubbles in the final cure. Make sure the bottles are well closed. Do not let the resin overheat (warm, not hot). If the resin overheats in the spa, your pot time will be severely compromised and the resin may not cure correctly. To give your resin the spa treatment, you can use a bowl with very warm, not hot, water or an electric salsa pot for no more than 5-10 minutes. If you’re in a warmer environment, you can omit the spa treatment.

Even with inclusions, coasters take a lot of resin so we need to mix a larger amount than we did for the small molds. The coaster mold we’re using holds a total of 2 ½ ounces of resin. The resin items we’ll be putting into the molds will displace some of that resin, reducing the amount of resin the molds will require. I’m mixing a bit more than 3 ounces (100 ml) of resin for both of the molds. I use the ml marks on my resin cups because they’re easier for me to see as I am pouring.

1. In the first cup, pour in enough of Part A (clear liquid) to reach the 50 ml mark.
2. In the second cup, pour in enough of part B to also reach the 50 ml mark.

3. Pour the part B cup into the A cup.
4. Using a stir stick, scrap the sides of the part B cup to make sure you get all of part B into the A cup.
5. Using that same stick, slowly stir the resin to mix the parts. Stirring slowly helps to reduce the inclusion of bubbles.
6. Be sure to scrape the side of the cup and scrape the stir stick from time to time as well.
7. When the mixed resin has gone from cloudy to clear, 2-3 minutes of slow stirring, it’s mixed. Slow and steady wins the race.
8. Then pour the mix into another cup and mix for at least 1 minute more to ensure all of the resin is completely mixed and none at the bottom of the cup was missed.

Pouring in the First Layer of Resin

To start the coaster, pour a small amount of resin into the mold.

To evenly coat the bottom of the mold, you can tip it slightly from side to side. At this point you want only about 1/8” to cover the bottom of the mold.

Adding the Leaves

For the leaves mold, we’re going to have the side of the mold facing up to be the finished top of the coaster. This means we’ll be placing the leaves so they’re facing us as we work.

Pour a small amount of resin into a small cup. Using a small cup for the next stage is much more manageable than a large one.

Drop one of the resin leaves into the small cup and spoon resin over it with the stir stick. Covering an inclusion with liquid resin helps to avoid trapping bubbles when putting it into the mold. The liquid on the inclusion will ‘meet’ the other liquid and flow together pushing away bubbles from under the inclusion. An inclusion is anything you’re ‘including’ in a resin casting. Resin leaves are the inclusion for this coaster.

Once it’s coated with liquid resin, pick the leaf up with your stir stick and slip it into the mold, into the thin layer of resin.

Be careful not to trap any bubbles beneath the leaf as you move it into position.

Add more resin leaves, first bathing each in resin. Use your stir stick to move them around in the mold as desired.

Continue adding leaves. If you took a picture earlier when you were dry fitting them in the mold, you can use it now to arrange them similarly. Push down the leaves to make as flat a surface as possible. Make sure you do not have any leaves poking up higher than the sides of the mold. You can use the paper across the top now, too, but be careful not to dip it into the resin. Getting resin on the paper won’t ruin the casting, but it will make your paper unusable.

Pouring on Additional Resin

After you have arranged the leaves, you want to pour in enough resin to cover them but not so much that it overfills the mold. Pour the resin to about 1/8” below the lip of the mold. Use your stir stick to push down any of the leaves that are too high or that might have decided to float.

 Shells Mold

Going back over to the shells mold. For this mold, we’re going to have the side facing the table as the finished top of the coaster.

Repeat Step 5 above to add a thin layer of resin to this mold as well. For this mold, since we’ll be adding in some rounded items, make that first layer about 1/4” to have a bit more liquid for the shells to sit in.

Just as with the leaves, coat each shell with resin before you put it into the mold. Place the shells so their back is facing you. If you have other resin shells than the ones we cast in the first tutorial, you can add them as well.

Once you have the shells placed, like the leaves mold, pour in additional resin but stop at about 1/4” from the top so we can add a ‘sand’ level later. If any of the shells is above the line of the resin, when we add the ‘sand’, they’ll look sunk in a bit rather than sitting on the ‘sand’.

Popping Bubbles

To help reduce the inclusion of bubbles in the resin, you can use a heat tool (such as one used for heat embossing on cards) or lighter to encourage bubbles to rise to the top. Many bubbles will pop on their own. You might have to use a tooth pick or the edge of a clean stir stick to encourage bubbles congregating on the sides to pop. When you have inclusions in the resin, it’s doubly important to follow this step as bubbles can get trapped in the shapes.

Just as with the leaves, coat each shell with resin before you put it into the mold. Place the shells so their back is facing you. If you have other resin shells than the ones we cast in the first tutorial, you can add them as well.

Set to Cure

Cover your molds and wait for the resin to cure. It is always best to cover your curing resin because you don’t want dust or cat hair or other unwanted things to become part of your project.

With Easy Cast, the cure time to unmolding is a minimum of 12 hours after the last resin was added.

Add Sand to the Shells Coaster

We’re going to give the shells some sand to ‘sit’ on. Since we’re building the coaster from the front to the back, we have to add the back when there won’t be any chance of it sinking down to become part of the front of the finished piece.

After the Shells coaster has been curing at least 4-5 hours (if you’re using Super Clear, at least 2-3 hours), the resin should be firm but can be sticky. This is a soft cure stage and a good time to add more since it will stay ‘behind’ everything we included earlier.

TIP: You can do this step after the first layer is fully cured for exactly the same effect. The two layers of resin will create a permanent bond.

Before adding the next layer is also a good time to flip over the mold and look through the clear plastic to get an idea how the coaster will look. Do not remove the coaster from the mold and be careful not to break the seal at this time. If there is air between the cured resin and the mold, the new resin will flow into that space and ruin the project.

To add another layer, we have to mix up a brand new batch of resin. Since this is going to be a small area, we can use the small cups and mix up just an ounce of Easy Cast. Make no less than the minimum recommended by the instructions that came with the resin.

Like we did before, pour a thin layer of resin on to the soft cured resin. Be sure to get the backs of each of the shells wet with the new resin. This will help reduce bubbles and get the next layer where we want it.

For this project, I was going to use real sand but didn’t have any on hand (or rather couldn’t find the sand I am sure I still have stashed somewhere) so I made faux sand from mixing a couple colours of Pearl Ex and adding in some chunky glitter. Real sand would work the same way as this faux sand.

Pour a small bit of the resin into another cup. You don’t want to just dump the sand into your main mixing cup because you want to have more control over how much resin and how much sand you’re combining. Plus, if you dump the sand in to the main cup, if you have resin left over, you can’t really do anything else with it.

Add the sand to the second cup and, with a second stir stick, slowly stir to combine the sand with the resin. Try not to introduce bubbles into the mixture. When the sandy resin is ready, it will look a lot like watery mud or a slurry.

Pour the sandy resin into the mold over the shells.

Continue filling the mold with sand and resin until it is about 1/8” from the top edge. This helps to avoid overfills. If there are still bits sticking up, don’t worry. There are a couple more steps left.

Just as before, use a heat tool to pop any bubbles and then set the coaster to cure

Removing the Coaster from the Mold

After more than 12 hours after the last resin pour, the coaster should be ready to unmold. Remember that we poured additional resin into the Shells coaster. It will be ready to unmold later than the Leaves coaster. When using Easy Cast, I usually wait until the next day to unmold.

Carefully bend the mold a little to start a line of air around the edge of the mold. You can press from the centre back of the mold as well. Continue lightly bending the mold until you can lift part of the coaster free. Because we used mold release at the start, the coaster should come out without a lot of effort.

When you bend a plastic mold to release cured resin, you don’t want to twist it so hard it bends out of shape, just enough to break the seal between the mold and the cured resin. Sometimes a whack on a hard surface, like a desk, can help break the seal, just like when you need to break the seal on a new jar of jam. A single whack is usually enough. If the seal still doesn’t want to break, you can put the mold with the stubborn resin into the freezer for 10-15 minutes. When you take it out, give it a whack on the counter or desk. Once you start to see a bubble of air between the mold and the cured resin, you’ve won.

Taking care of the casting edge

When you cast in a mold and don’t fill to the absolute top of the edge or dome, the resin will cure ever so slightly concave. This will leave a sharp and potentially uneven edge all around that’s difficult to show in pictures but your fingers will definitely feel it.

You can carefully cut away the majority of the sharp edge with a sharp pair of scissors. The resin is pretty thin in this location and can be simply cut away. Make sure you cut around the mold evenly.

You can also sand the edge. A nail sander from the dollar store works great because it’s an easy shape to hold in your hand and the sanding surface is not too coarse. You generally don’t want anything coarser than 400 grit.

Be sure to wear safety glasses any time you are sanding resin. It’s also best to wear a paper breathing mask to avoid inhaling any of the resin dust.

Sanding to Flatten the Coaster

After taking off the edge, you should do a ‘tip test’ to see how flat the coaster is to determine what other steps we might need to do.

Put a water bottle or cup on the resin and try to tip the item from side to side. If it doesn’t rock, then the coaster is flat enough. If it does rock, you’ll need to do something to make it flatter, either add a small coating of more resin, similar to doming, or sand off the bits that stick out.

On the Shells coaster, a couple of the shells extend further than the ‘sand’ layer. This can be detected in the tip test and also just by looking from the side. Since the bottom of the shells are sticking out the back, let’s sand them down a bit.

When sanding a large area of resin, not only can it create a large amount of resin dust, but the friction can heat up the resin and cause an unsightly effect (I haven’t had that happen but still don’t risk it). You can use waterproof sandpaper and sand the piece in a pool of water which both contains the dust and cools the friction heat. A cheap foil pan works great for this.

WARNING: If any item is used with uncured or resin dust, it is unsafe to use it with food after.

For best results, sand the piece by moving it over the sand paper in a figure 8. When the bottom is smooth, be sure to run the sand paper along that bottom edge as well to make sure it’s smooth.

Only sand to flatten on the back side of your coaster. If you need to flatten the top and want to preserve the inclusions that might be protruding a little, you can add a small layer of resin similar to a doming technique. Thankfully my Leaves coaster passed the tip test, but other issues did need to be corrected.

Adding a Cork Base

Since the Shells coaster has an opaque bottom, but the sandy side isn’t as attractive as the shell side, this is a perfect time to add a cork bottom. This has the added benefit of having a cork bottom, it will be less likely to scratch any surface and will stay put easier. You could use felt for this instead. You can often find low-cost cork or felt sheets at a dollar store or craft store.

Trace the mold on to the cork with a pen or pencil and then cut it out on the inside of the line.

Slather the cork disc with craft glue. One that will dry waterproof is best. Be sure to get the glue out to the edges and not too thick.

Place the cork disc on to the back side of the coaster and press firmly to adhere well.

Adding Clear Dots

After the Leaves coaster is fully cured (another 12 hours after the last pour), we can finish it, too.

To preserve the clear look of the Leaves coaster, we’ll add some clear dots “bumper pads” to the bottom. Like the cork on the Shells coaster this will help prevent the coaster from scuffing surfaces and keep it from moving. You can buy bumper pads at hardware stores, craft stores, or many other locations usually in the area of the store that has hardware for hanging pictures or cabinet doors.

Most bumper pads are self-adhesive. Just peel them off and stick them where you want. You can place 3 or 4 around the edge of the coaster, roughly equidistant from each other. Since we’re aiming for a clear look on the Leaves coaster, I placed them mostly behind the opaque leaves. You want the pads to be evenly spaced so the coaster doesn’t rock when something is placed on it.

Finished items

Ta da! We now have 2 coasters made with resin items we cast earlier (using the previous tutorial) and made 2 styles using the same mold. This tutorial covered a lot of techniques too while learning how to make resin coasters.

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